1022 
Journal of Agricultural Research 
Vol. V f No. 22 
temperature and relative humidity 
The determination of the effect of varied temperature and relative 
humidity on the opening of the stomatal pore of the sugar-beet plant 
was made under conditions which were somewhat under control. The 
plants used for study were first-year beets about 3 months old and of 
thrifty growth which had been grown in a deep soil bed in the green¬ 
house at Rocky Ford, Colo. A good root development was thus made 
possible, and normal leaf production had been accomplished. The 
leaves used for the readings were all mature and averaged about 14 cm. 
wide and 20 cm. long. Direct readings of the widths of the stomatal 
pores were made on plants both left free in the greenhouse and kept 
covered during the time of the experiment with a large glass humidity 
box (PI. LXXX, fig. 2) of about 20 cubic feet capacity. This box 
was five-sided and could be placed over plants in a manner comparable 
to the bell-jar method. Aeration was made possible by this means 
and room was also available for a hygrothermograph, so that constant- 
humidity and temperature records were available without any dis¬ 
turbance of the plants. Comparable hygrothermograph records were also 
kept among the leaves freely exposed in the greenhouse and both instru¬ 
ments were checked by means of a cog psychrometer (PI. LXXX, 
fig. 2). Middle-blade portions of different leaves were taken from all 
plants and stomatal readings made by the “in situ” method. The 
definite data of the experiments conducted on May 16, 17, and 20 and 
June 3 are given in Table VII and the graphic representations in figures 
2 to 5. 
Table VII.— Effect of varied temperature and relative humidity on stomatal pore open¬ 
ing on sugar-beet leaves at Rocky Ford, Colo., in IQI3. Comparable readings were 
taken in the greenhouse on plants covered by a large glass humidity box and on those 
left freely exposed to ordinary greenhouse conditions 
In hiunidity box. 
In greenhouse. 
Date and time of 
reading. 
Tem¬ 
pera¬ 
ture. 
Rela¬ 
tive 
hu¬ 
midity. 
Average stomatal 
pore widths.® 
Upper 
leaf 
surface. 
Lower 
leaf 
surface. 
Tem¬ 
pera¬ 
ture. 
Rela¬ 
tive 
hu¬ 
midity. 
Average stomatal 
pore widths.® 
Upper 
leaf 
surface. 
Lower 
leaf 
surface. 
May 16: & 
9. 00 a. m 
1. 30 p. m 
4.15 p.m. 
7.00 p. m 
May 17 : c 
5.00 a. m. 
7.15 a.m, 
8. 30 a.m. 
10.00 a. m. 
n. 00 a. m 
1.30 p.m. 
4.20 p.m. 
°F. 
68 
93 
89 
7 i 
Per ct. 
70 
46 
54 
79 
9-o ( 5 ) 
12.6 (4) 
8-6 (5) 
o (5) 
5 i 
60 
63 
73 
80 
79 
70 
95 
67 
66 
65 
63 
60 
74 
•36 
6.8 
7-3 
6.8 
7. a 
7. 2 
7.2 
2. 7 
8.2 
7-5 
9 
7.2 
6.4 
$ 
Q F. 
77 
90 
93 
75 
52 
67 
7 i 
78 
83 
80 
7 i 
Per ct. 
43 
16 
18 
24.5 
o 8 ai 
c $ 
o 
o 
o 
o 
73-5 
58 
50 
38 
31 
32 
34 
o 
1. 8 
2 - 5 
5-4 
1.8 
7.2 
o 
(5) 
(3) 
(9) 
U) 
(6) 
(3) 
(4) 
a The number of readings is given in parentheses following each average. 
6 The sun shone brightly throughout the entire day. 
c The sun shone brightly up to 4 p. m. 
